Investigations into the decline of two important sport fish, walleye and yellow perch, in New York`s Oneida Lake showed that the likely causes were an increase in cormorant numbers coupled with ecological changes associated with zebra mussel introduction and variations in the abundance of alternative forage fish. Management response included cormorant control and size limits. Walleye are now recovering as predicted from model evaluations of the interactions between cormorants and fish. Increased early mortality for both fish species also contributes to current population dynamic but our evaluation of stocking walleye fingerlings or yearlings show that this is not a viable option in Oneida Lake.

Walleye and yellow perch are the main sport fish in Oneida Lake and represent the largest New York sport fishery in a single lake outside of the Great Lakes. The populations of both species have been declining since the early 1990s. Reversal of this trend requires an understanding of the causes of the decline.

The long-term data collections on fish populations, particularly walleye and yellow perch, in Oneida Lake allowed us to investigate the effect of ecological change on these two populations. We identified the increase in piscivore birds, namely double-crested cormorants, as one of the causes. Increased fish mortality during the first year of life is also a contributing factor. This detailed analysis was possible only because of the long-term data on different age groups of fish, data that is rarely available in affected lakes. We now concentrate on analysis of indirect effects and increased early mortality in both fish species using both data and model analyses.

Our results contributed to management action to decrease the number of cormorants on Oneida Lake and Lake Ontario as well as in the province of Ontario and the states of Wisconsin and Minnesota. In Oneida Lake, the management actions coincide with an increase in abundance of both walleye and yellow perch in Oneida Lake, and substantially higher angler use and catch rates. Sport fishing is important for tourism in the region and Oneida Lake has the fourth-largest sport fishery in New York state (following Lake Ontario, Lake Erie, and the St Lawrence River).

Fisheries